1. Field of the Invention
The present invention relates to a crown control compensation controlling method capable of automatically compensating for variations in plate thickness caused by crown control and effecting a stable control in a multiple roll mill for rolling thin plates such as nonferrous metals and special steels.
2. Description of the Prior Art
As an actuator for controlling the shape of a rolling stock being rolled by a multiple roll mill there is a crown control device. It is known that, if this device is operated, there will arise a change in roll gap, which causes a variation in plate thickness.
Therefore, where such crown control device is operated to control the shape of a rolling stock, it is necessary to perform operations gradually in consideration of a response from a thickness gauge so as not to exert a bad influence on the plate thickness.
On the other hand, a wedge type hydraulic reduction device has been applied to a multiple roll mill. This device makes a high-speed control for roll gap and effects an automatic plate thickness control as disclosed in Japanese Patent Laid-Open Publication No. 9707/83. For this automatic plate thickness controller there is adopted a constant gap control or a feed forward control to obtain products with a high accuracy of plate thickness.
According to the prior art, however, variations in plate thickness caused by crown control are corrected only by feedback of a thickness gauge monitor, so during the period corresponding to the delay time of the feedback, the plate thickness becomes off-gauge, thus making it impossible to effect a high-speed control for obtaining a rolled product which is satisfactory in both shape and thickness.